The difference of the capacity to induce immune responses in different strains of mice infected with Plasmodium yoelii

To clarify the difference of the capacity to induce immune responses in different strains of mice infected with Plasmodium yoelii,DBA/2 and BALB/c mice were infected by intra-peritoneal injections of P.yoelii strain 17XL parasitized erythrocytes and the parasitemia of individual mice was monitored by microscopic examinations of blood smear stained with Giemsa's stain. Mice from infected and normal groups were sacrificed at indicated times to collect sera and spleen cells for study. The levels of IFN-γ and IL-12 in sera were measured by ELISA kits, and level of NO in spleen cell suspensions was assayed by Griess reaction.It was found that the level of parasitemia in DBA/2 mice was lower in comparison with that in BALB/c mice, and accordingly, DBA/2 mice survived by 20 postinfection days, while all the BALB/c mice after peak level of parasitemia. In addition, significantly increased levels of IFN-γ and IL-12 could be demonstrated in DBA/2 mice from 1 to 20 postinfection days. Although increased levels of IFN-γ and IL-12 could be also demonstrated in BALB/c mice, but they decreased significantly from 3 to 6 postinfection days. A continuously increased level of NO could be observed from 3 to 6 postinfection days in DBA/2 mice, while this was not observed in BALB/c mice.It is concluded from the above mentioned data that DBA/2 mice can inhibit or clear up parasitemia through establishment of the Th1 type of cellular immune responses in the early stage of P.yoelii infection, in which IL-12 plays a critical role in the initiation and maintenance of the Th1 type of immune responses.